1. Field of the Invention
The invention relates to a method of forming a resist pattern, which improves an OPE characteristic generated by the difference between sparse and dense mask patterns and has high fidelity to the design of the pattern, and a method of manufacturing a semiconductor device using the method of forming the resist pattern.
2. Description of the Background Art
With high integration of semiconductor devices, a method of manufacturing a semiconductor that is suitable for a micro process has been studied and developed. However, deterioration of fidelity to the design of the pattern based on the optical proximity effect (referred to as “OPE” below) by adjacent patterns has been a problem, and the OPE characteristic is an important parameter in miniaturization.
In photolithography, it is known that multiple interferences of light occur in a resist film, and the dimensional width of the resist pattern changes along with changes in the resist film thickness. The multiple interferences of light occur as a result of irradiated light that is incident on the resist film formed on the substrate interfering with the reflected light from the substrate, and the amount of optical energy absorbed in the thickness direction of the photoresist film differs.
As described in Japanese Patent Laying-Open No. 08-015859, a method of forming an anti-reflective film on the substrate as a means of reducing multiple interfering actions of light in the resist film is conventionally known. The conventional method of forming a resist pattern in which the anti-reflective film is formed on the substrate is shown in FIGS. 9A to 9F. In this method, first, as shown in FIG. 9A, an anti-reflective film 92 is formed on a semiconductor substrate 97, and then a resist film 91 is spin-coated, and next, as shown in FIG. 9B, resist film 91 is baked and hardened. Continuously, as shown in FIG. 9C, an exposure process is performed through a mask 93, and after exposure, as shown in FIG. 9D, it is baked. Then, as shown in FIG. 9E, it is processed with a 2.38% alkali developer 94, and a fixed resist pattern 95 as shown in FIG. 9F is obtained. Although the interfering action can be reduced to some degree by anti-reflective film 92 on substrate 97, the OPE can not be improved sufficiently.
In order to prevent in-film multi-reflection inside the resist or to prevent the deactivation of an acid of a chemical amplification type resist due to amine in air, as described in Japanese Patent Laying-Open No. 07-295228, a method of forming an upper layer film of a water-soluble polymer on the resist is known. In the chemical amplification type resist, there is an acid catalyst type resist in which an acid is generated in the exposed part as a catalyst, and it is a resist with high sensitivity and high resolution because the catalyst is used. However, after exposure and before baking is performed, the acid catalyst generated in the exposed part becomes inactive due to the influence of a small amount of amine which exists in air, and the line width and resolution of the resist change. It is considered that the formation of the upper layer film is effective in preventing such a PED (Post Exposure Delay) phenomenon.
The conventional method of forming a resist pattern in which an upper layer film is formed is shown in FIGS. 10A to 10H. First, as shown in FIG. 10A, an anti-reflective film 12 is formed on a substrate 17, and then a resist film 11 is spin-coated, and next, as shown in FIG. 10B, the resist film 11 is baked and hardened. Continuously, as shown in FIG. 10C, after an upper layer film 16 is formed on a water-soluble polymer, it is baked and hardened as shown in FIG. 10D. Next, as shown in FIG. 10E, an exposure process is performed through a mask 13, and after exposure, as shown in FIG. 10F, it is baked. Then, as shown in FIG. 10G, it is processed with a 2.38% alkali developer 14, and a fixed resist pattern 15 as shown in FIG. 10H is obtained. However, because the upper layer film formed in such a manner is water-soluble and does not penetrate into the resist, and a mixing layer is not formed, the OPE characteristic generated by the difference between sparse and dense resist patterns can not be improved (Jeng-Horng Chen et al., “Characterization of ArF immersion process for production”, Optical Microlithography XVIII, edited by Bruce W. Smith, Proceedings of the SPIE 2005, Vol. 5754, pp. 13-22).